Heretofore, in a case of producing a rubbery polymer from an aqueous latex of rubbery polymer particles, it has been practiced a method of at first obtaining a coagulate by various methods and then removing water or solvent from the coagulate followed by drying.
As a method of obtaining the coagulate, it has been proposed, for example, (1) a method of adding an inorganic electrolyte or acid as a coagulant, (2) a method of adding a nonionic polymer coagulant), (3) a method of bringing an organic solvent into direct contact with a latex, (4) a method of heating or freezing a latex, (5) a method of providing mechanical shearing force, or a method of appropriately combining them.
In this case, as a measure for removing an emulsifier and an electrolyte derived from the polymer and, further, impurities such as an inorganic electrolyte used as the coagulant from the obtained coagulate, a method of bringing the coagulate into contact with water has been adopted generally. However, for removing such impurities, not only a great amount of water is necessary but also impurities can not be removed sufficiently at present. Further, a method of cleaning by an organic solvent has also been used, but this complicates the steps to make the process industrially disadvantageous.
On the other hand, cured products of polymerizable organic compounds having reactive functional groups, for example, cured products of epoxy resins are excellent in various aspects such as dimensional stability, mechanical strength, electric insulation property, heat resistance, water proofness and chemical resistance. However, cured products of epoxy resins have low fracture toughness to sometimes show extremely brittleness and such nature often results in problems in wide range of application uses.
As one of methods for solving the problems, it has been attempted toblenda rubbery ingredient in an epoxy resin. Among all, a method of blending a rubbery polymer previously prepared into a particulate shape by using, for example, a polymerization method in an aqueous medium typically represented by emulsion polymerization, re-dispersion polymerization or suspension polymerization is considered to provide various advantages compared, for example, with a method of dissolving and mixing non-crosslinked indefinite rubber ingredient to an epoxy resin and then causing phase separation in the curing process thereby forming a dispersion phase of the rubber ingredient in an epoxy resin cured product continuous phase, such that the state of dispersion is less changed depending on the blending and curing conditions, in principle, and the rubber ingredient does not intrude to the continuous phase of the epoxy resin cured product by previously crosslinking the rubber ingredient thus causing less lowering of the heat resistance and the rigidity, and various production processes have been proposed.
For example, (6) a method of heating apartially cross linked rubbery random copolymer particles prepared by emulsion polymerization using a nonionic emulsifier or the like to a temperature higher than a cloud point of the emulsifier, thereby coagulating them, then optionally washing the coagulate with water and mixing the same with an epoxy resin (for example refer to JP Nos. 1708498, 2751071, and JP-A No. 5-295237), (7) a method of mixing a rubbery polymer latex and an epoxy resin and then evaporating off a water content to obtain a mixture (for example, refer to JP-A No. 6-107910), and (8) a method of mixing a rubbery polymer latex with an epoxy resin under the presence of an organic solvent to obtain a mixture (for example, refer to the specification of U.S. Pat. No. 4,778,851) are disclosed.
Since the method (6) described above is a method of obtaining a coagulate by the use of a coagulant, mainly, an inorganic electrolyte, impurities such as an emulsifier which is deposited to the polymer or confined in the coagulated polymer upon coagulation can not be removed sufficiently while a greater amount of water is used at present. Further, since the rubbery polymer particles are intensely adhered to each other by coagulation also including coagulation by heating, it requires pulverization or re-dispersion operation with a considerable large mechanical shearing force upon mixing with the epoxy resin, and it is often difficult to uniformly re-disperse the rubbery polymer particles in the epoxy resin while a larger amount of energy is used.
In the method (7) above, impurities such as emulsifier and electrolyte derived from the polymer are left as they are and, in addition, since the epoxy resin is only slightly soluble in water, even when a considerably large mechanical shearing force is applied, it still leaves a not-yet-mixed portion, and lumpy coagulate are sometimes formed in the not-mixed portion.
Since the method (8) described above does not include coagulating operation, an epoxy resin composition with the rubbery polymer being re-dispersed uniformly can be obtained easily, but a great amount of water content present together with the organic solvent in the system (mixture) (the water content more than the amount which the organic solvent can solve) has to be separated or evaporated off. However, separation of the organic solvent layer and the aqueous layer requires much time such as one day and one night, or the organic solvent layer and the aqueous layer are difficult to be separated substantially since they form a stable emulsified suspension. Further, in a case of removing the water content by evaporation, a great amount of energy is necessary and, in addition, water soluble impurities such as an emulsifier or sub-starting materials usually used in the production of rubbery polymer latexes remain in the composition to degrade the quality as well. Accordingly, removal of the water content is troublesome in any of the methods of separation or removal by evaporation, which can not be said industrially preferred.
An object of the present invention is to provide, as a process for producing rubbery polymer particles refined from an aqueous latex of rubbery polymer particles, an efficient production process of obtaining a loose flocculate from the rubbery polymer particles obtained in the state of an aqueous latex without using a coagulant under the presence of an organic solvent and discharging the impurities to the aqueous phase and, preferably, provide a further efficient production process capable of reduce the cost of equipment by a continuous processing. Further, it intends to provide a process for producing a resin composition conveniently and efficiently that can uniformly mix and disperse rubbery polymer particles in a polymerizable organic compound having a reactive functional group thereby remarkably decreasing impurities such as an emulsifier or an electrolyte derived from the polymer particles, by re-dispersing a loose flocculate again in the organic solvent and mixing the same with the polymerizable organic compound having the reactive functional group.